1. Technical Field
This description generally relates to the field of electronic devices and, in particular, to electromagnetic interference shielding of electronic devices.
2. Description of the Related Art
Electronic devices commonly require electromagnetic interference (EMI) shielding to prevent disruption of their performance due to electromagnetic fields in their operating environment. An EMI shield is typically one of a variety of metal containers that envelops an electronic device and is electrically connected to a ground reference of the device. The shield limits penetration of an EMI field to a circuit of the device by attenuating the EMI field before it reaches the device. The particular EMI shield selected for a device typically depends on the type of device requiring shielding.
For packaged electronic devices, including ball grid array (BGA) electronic packages, one known shielding method uses sputtering. Sputtering, also known as chemical vapor deposition (CVD), deposits a metal film directly on the body of the package. The metal on the body is electrically connected to a ground conductor, thereby isolating the electronic circuit of the device from electromagnetic radiation outside the shield. The CVD process has the benefit of providing the device with a compact shield, which avoids an undesirable increase in device size due to the shield. However, CVD is relatively expensive to implement and therefore increases the cost of the device.
A second known method for EMI shielding of electronic devices is a metal plate, as shown in FIG. 1. The metal plate is sized and shaped to fit over a board-mounted electronic device. Typically, the metal plate has sidewalls at its edges to mount the plate to the same PC board that the device is mounted on. The metal plate is electrically connected to a ground conductor on the PC board to ground the plate. Although inexpensive to produce, the technique has the disadvantage of increasing the overall size of the electronic package.
A third known method for EMI shielding, and one used for EMI shielding of camera module assemblies, is a shield can, as shown in FIG. 2. The camera module assembly may include a lens and a circuit on a substrate. The lens includes an aperture in which an image can be received. As with the electronic device metal plate shield described above, the shield can is sized and shaped to fit over the camera module. The metal can may be connected to the same PC board that the device is mounted on or connected to the ground pad of the device as shown in FIG. 2. One difference from the metal plate EMI shield is that the can has an opening over the lens aperture to allow an image to pass through the can to the lens.
The shield is typically constructed from a thin pre-formed sheet of metal. There were various ways known in the prior art to attach the metal can to the substrate to provide for EMI shielding depending on module configuration. According to one known technique, the metal can is coupled with conductive glue to the PCB. While this method provides sound EMI shielding, the method increases the module assembly size and also increases production cost due to the complexity of the assembly process.